This invention relates generally to semiconductor integrated circuits fabricated as a plurality of die in a semiconductor wafer, and more particularly, the invention relates to the testing of die in a semiconductor wafer.
Semiconductor integrated circuits are fabricated as die in a semiconductor wafer using photo resist masking, chemical etching, and dopant implantation and diffusion techniques. Once the dice are completed and tested, the wafer is scribed and broken to obtain individual integrated circuit chips.
Before scribing and breaking the wafer, each individual integrated circuit is electrically probed and tested for functional integrity. Each die has input/output (I/O) pads along the periphery of the integrated circuit chip which are engaged by test heads having probes which contact the I/O pads.
As devices get more complicated, more and more bond pads are needed on the die. These pads are typically placed on the perimeter of the die for wire bonded and tape bonded packages. With a particular size of die, the number of bond pads that can be placed on the die is limited by the separation or pitch of the pads. One of the methods of getting the largest number of pads on a particular die is to decrease the separation or pitch of the pads, the smallest pitch being limited by the ability to test and bond to the die.
The pitch of the pads on a particular die are limited by the capability of testing the pads. In die testing, probes are used to contact the pads, and as the pitch of the pads gets smaller the probes have to be made smaller and positioned closer. This increases the difficulty of manufacturing the probes and the cost thereof. Further, as the probes get smaller, the current carrying capacity of the probes decrease and limit the test capability of the die.
Thus, the limit on the probe pitch limits the size of the die for a given number of bond pads. This can mandate a larger die than is required in the design and thus increases the cost of the die. As the probes get closer, the cost of making the probe cards increases, and the finer probes needed for fine pitch probing limits the current carrying capacity of the probe, thus reducing the effectiveness of testing the die.